ANS Flashcards
Does the ANS control voluntary or involuntary functions?
What is the term for this?
Involuntary (or visceral)
How does activation of ANS mainly occur?
- Hypothalamus
- Brainstem
- Spinal cord
3 Divisions of the ANS
Which is independent of the other two divisions?
- Sympathetic
- Parasympathetic
- Enteric
Enteric (GI function) is independent from other two
Are most target organs innervated by either the sympathetic or parasympathetic branches?
No, most have innervation from both SNS and PNS and activity is a balance between the two
Effect of SNS and PNS on SA node?
SNS- increases HR
PNS - decreases HR
Effect of SNS and PNS on AV node
SNS- increases conduction velocity
PNS- decreases conduction velocity
Effect of SNS and PNS on His-Purkinje system
SNS- increases automaticity and conduction velocity
PNS- minimal effect
Effect of SNS and PNS on ventricles
SNS- Increases contractility, conduction velocity, and automaticity
PNS- minimal effects, slight decrease in contractility)
Effects of SNS and PNS on Bronchial smooth muscle
SNS- relaxation
PNS- contraction
Effect of SNS and PNS on GI motility
SNS- decreases motility
PNS- increases motility
Effect of SNS and PNS on GI secretions
SNS- decreased secretion
PNS- increased secretion
Effect of SNS and PNS on GI sphincters
SNS- contraction of sphincters
PNS- relaxation of sphincters
Effect of SNS and PNS on gallbladder
SNS- relaxation of gallbladder
PNS- contraction of gallbladder
Effect of SNS and PNS on bladder smooth muscle tone
SNS- Relaxation of bladder smooth muscle
PNS- Contraction of bladder smooth muscle
Effect of SNS and PNS on bladder sphincter tone
SNS- contraction of bladder sphincter
PNS- relaxation of bladder sphincter
Effect of SNS on radial muscle of eye
SNS- mydriasis (muscle contraction)
Pupil dilation
Effect of PNS on sphincter muscle of eye
PNS- miosis
Effect of SNS and PNS on ciliary muscle of eye
SNS- relaxation for far vision
PNS- contraction for near vision
Effect of SNS and PNS on liver
SNS- glucogenolysis and gluconeogensis
PNS- glycogen synthesis
Effect of SNS on pancreatic beta cell secretion
SNS- decreased pancreatic beta cell secretion
Effect of SNS and PNS on salivary gland secretion
SNS- increased salivary gland secretion
PNS- marked increase in salivary gland secretion
Effect of SNS on sweat glands
SNS- Increased secretion
Effect of SNS on apocrine glands
SNS- increased secretion
Effect of SNS and PNS on coronary arterioles
SNS- Constriction (alpha) and relaxation (beta)
PNS- Relaxation (?)
Effect of SNS and PNS on skin and mucosal arterioles
SNS- constriction
PNS- relaxation
Effect of SNS and PNS on skeletal muscle arterioles
SNS- constriction (alpha) and relaxation (beta)
PNS- relaxation
Effect of SNS and PNS on pulmonary arterioles
SNS- constriction
PNS- relaxation
Where do sympathetic nerves arise from?
T1-L2 segments of spinal cord
Where do parasympathetic nerves arise from?
Cranial nerves III, V, VII, IX, and X
Sacral spinal cord S2, S3 and sometimes S1, and S4
Where are sympathetic preganglionic neurons located?
Intermediolateral horn of spinal cord
Where do sympathetic preganglionic fibers leave from and go to?
Leave with the ventral nerve roots and go into one of the 22 pairs of ganglia in the paravertebral sympathetic chain
Where do preganglionic sympathetic neurons synapse? What may happen before this?
Synapse with cell bodies of postganglionic fibers at the paravertebral chain
Some may stay at the same level, but most travel cephalad or caudad prior to synapsing
Where do postganglionic fibers go to after exiting the paravertebral chain?
Target organs
Describe preganglionic fibers
Mostly myelineated
Fairly slow B-fibers
Coming out of the white ramus
Describe postganglionic fibers
Mostly unmyelinated C fibers
What cranial nerves supply the head?
Cranial Nerve III, V, VII, IX
What nerve supplies 75% of all parasympathetic nervous system fibers (particularly the thorax and abdomen)?
Cranial nerve X (Vagus)
What nerves supply the pelvis?
S2, S3
Sometimes S1 and S4
What is the difference in lengths of pre and postganglionic neurons between the PNS and SNS?
- PNS: has longer preganglionic and very short postganglionic neurons
- SNS: short preganglionic, long postganglionic
What neurotransmitter do all preganglionic neurons release?
What does it activate?
Acetylcholine
Activates both SNS and PNS postganglionic fibers
What neurotransmitter do PNS postganglionic neurons release?
Acetycholine
What neurotransmitter do most SNS postganglionic neurons release?
What is the exception?
Most release norepinephrine
Exceptions are sweat glands and some blood vessels release acetylcholine
What are some other neurotransmitters of the ANS besides acetylcholine and norepinephrine?
- Dopamine
- Vasoactive Intestinal Polypeptide (VIP)
- ATP
- Neuropeptide Y
How is norepinephrine synthesized?
Synthesized from phenylalanine and tyrosine by a series of enzymatic-controlled steps
Progression from tyrosine to epinephrine
Tyrosine–> dopa –> dopamine –> norepinephrine –> epinephrine
Which circulates longer, acetylcholine or norepinephrine?
Norepinephrine slightly longer
Circulating half-life of 2 minutes
What happens to 80% of norephinephrine?
80% undergoes reuptake back into postganglionic sympathetic nerve endings where it can be reused
What causes true termination of action of norepinephrine?
Dilution by diffusion from receptors
- Reuptake is what allows the concentration gradient for it to diffuse away
APEX says termination of effect is reuptake so its all very unclear
What drugs can block reuptake of norepinephrine?
What can this cause?
- Cocaine, amphetamines
- Can cause depletion of norepinephrine
What two enzymes metabolize norepinephrine?
Monoamine oxidase (MAO) and Catechol-O- methyltransferase (COMT)
Where is MAO located?
Intracellularly on the mitochondria of noradrenergic nerve endings
Where is COMT located?
Extracelluarly in many tissues, mostly in the liver
In a patient receiving ephedrine, what home medication could place the patient at risk for hypertensive crisis?
MAOIs
Ephedrine causes release of norepinephrine and MAOIs block the metabolism of norepi
How is acetylcholine synthesized?
Choline and acetyl coenzyme A by enzyme choline acetyltransferase
where is acetylcholine stored?
In synaptic vesicles
How is acetylcholine metabolized?
Rapidly by acetylcholinesterase to metabolites choline and acetate
T/F the enzyme that metabolizes acetylcholine is pseudocholinesterase
False
Acetylcholinesterase does
Which metabolite of acetylcholine undergoes reuptake into the nerve ending?
Choline
Does acetylcholine have short or long duration?
Short, due to highly efficient acetylcholinesterase
Is acetylcholine’s effect local or widespread?
Highly localized
Where are alpha1 receptors located?
Postsynaptic
In smooth muscle throughout blood vessels, GI tract, GU system, eye, lungs, and uterus
Effects of stimulation of alpha1 receptors on vascular smooth muscle (skin, mucosa, hepatorenal)
Contraction- aka vasoconstriction
Effects of stimulation of alpha1 receptors on heart, pupils and bronchial smooth muscle
- Increases force of heart contraction slightly
- Dilates pupils (contracts radial eye muscles)
- Bronchoconstricts
Effect of stimulation of alpha1 receptors on prostate and uterine smooth muscle, and sphincters of GI/GU tracts
Contractions
Effect of stimulation of alpha1 receptors on salivary and sweat glands
Secretion
Effect of stimulation of alpha1 receptors on insulin and lipolysis
Inhibits insulin secretion and lipolysis
How does activation of alpha1 receptors lead to contraction of smooth muscles?
Increases intracellular calcium ion concentration
General effect of alpha2 receptor stimulation?
Exception?
“Relaxation”
Exception is effect on postsynpatic receptors for vascular smooth muscle - causes contraction
Presynaptic Alpha2 receptor stimulation inhibits release of what NT?
Norepinephrine
Via negative feedback loop
Effects of postsynaptic alpha 2 receptor stimulation in CNS
Hyperpolarization
- Causes sedation, decreased MAC, decreased sympathetic outflow causing vasodilation and decreased BP
Effects of alpha2 receptor stimulation on platelets and insulin
Causes platelet aggregation and and decreased insulin release
Are alpha 2 receptors more pre or post synaptic?
How do they act?
Largely pre-synaptic, but both
Act via G protein subgroup Gi, inhibiting adenyl cyclase, reducing cAMP and calcium levels
Where are beta1 receptors located?
Postsynaptic in the heart
Stimulation of beta1 receptors produces what effect?
Inotropic, chronotropic and dromotropic effect
Define inotropic
Increased force of contraction
Define chronotropic
Affects heart rate
Define dromotropic
affects conduction velocity
Beta1 receptors effect on adenyl cyclase and cAMP
- increased andenylate cyclase
- Increased cAMP
Effect of beta1 receptors increasing cAMP
stimulation initiates cascading protein phosphorylation reaction and stimulates sodium-potassium pump
Where are beta2 receptors located?
Smooth muscle and glands, postsynaptic
Effect of beta2 stimulation on respiratory, uterine, and vascular smooth muscles
Relaxation
- Causes bronchodilation, vasodilation, relaxation of uterus and GI/GU
Effect of beta2 stimulation on skeletal muscle
Vasodilation- better perfusion
Effect of beta2 stimulation on ciliary muscle of eye
Relaxation allowing for far vision
Effect of beta2 stimulation on metabolic processes
- Gycogenolysis
- Lipolysis
- Gluconeogenesis
- Increased insulin release
Results in hyperglycemia
which dopamine receptors are presynaptic and which are post?
D1= postsynaptic D2= presynaptic
Effect of stimulation of D1 receptors
Vasodilation of renal, mesenteric, coronary, and cerebral blood vessels
Effect of stimulation of D2 receptors
Inhibit release of norepinephrine
Cause N/V
Cholinergic receptors within an ANS ganglion and at the NMJ
Nicotinic
Two types of cholinergic receptors
Nicotinic and muscarinic
Where are M1 receptors?
Autonomic ganglia and the CNS
Where are M2 receptors?
Principally in the heart and salivary glands
Where are M3 receptors?
Bronchial tree
What is unique about innervation of the adrenal medulla?
Innervated by preganglionic fibers that come directly from the spinal cord and bypass the paravertebral ganglia
What is released when SNS stimulation of adrenal medulla occurs?
Epinephrine (80%) and Norepinephrine (20%) directly into circulation
This means they act as hormones instead of NTs
Allows stimulation of areas that aren’t directly innervated by the SNS
Which branch of the ANS has more localized effects and which has more widespread effect?
PNS is more local
SNS is widespread (due to adrenalla medulla releasing hormones directly into circulation)
Effects of stimulation of adrenal medulla
Prolonged (10-30 seconds)
?
How does parasympathetic system effect MAP?
Chronotropic effects only (HR)
Practicing my vocab because TC says it matters
How does SNS effect MAP?
- PVR
- HR
- Contractility
- Venous tone
